<?php
const STR = 'Hello world!';

/**
 * @ref https://mp.weixin.qq.com/s?src=11&timestamp=1584270893&ver=2218&signature=vJvPgDdihCtdRnmznqBao-y8C8FgjW7f6CmWlaC9ZRHGoWq44a3LT*taADcPp0mIjirD8XnqU0*GwqQuZWyDHIsq32SDor3ukk5y9aI12Y94hNsDCYtfzOhBtKqzmos6&new=1
 */
function main()
{
    echo STR . PHP_EOL;
    echo STR, PHP_EOL; // `echo` is a language structure

    echo(STR . PHP_EOL); // Language structure is no needed for the parentheses, but SOME can be used like as a function. It is NOT a recommanded example.
    Echo(STR . PHP_EOL); // `echo` is a keyword. Keywords are case insensitive. It is NOT a recommanded example too.

    $func_name = 'echo';
    $func_name(STR);
}

main();
